The reason why only Jedi/Sith make and wield lightsabers is because they are the only people who can safely and effectively use them.
Lightsabers are not mass produced, and from the films I see no reason for thinking otherwise.
The extra lightsabers given to Anakin and Obi Wan could have come from anywhere. A council that has lasted for thousands of years gets through several generations of members, and many of them will have died from old age. So it's not hard to believe that extra lightsabers would collect in the cupboard.
As for Grevious having Obi Wan and Anakin's hilts in his collection; he obviously copied them after going online and seeing them as "Handle's of the month" in the "What Lightsaber?" magazine website.